The present invention relates to a photoresist (termed herein as xe2x80x9cresistxe2x80x9d) developing process, more especially to a developing process for preparing a resist pattern on a wafer by applying a puddling method in a process for preparing a semiconductor.
In a process for preparing a semiconductor, forming a resist pattern on a wafer is now put into practice by using, for example, an apparatus shown in FIG. 8. In FIG. 8. xe2x80x9c11xe2x80x9d denotes a wafer; xe2x80x9c12xe2x80x9d, a chuck for holding a wafer by absorption; xe2x80x9c13xe2x80x9d, a shaft of a chuck; xe2x80x9c14xe2x80x9d, a motor for rotating a shaft of a chuck; xe2x80x9c15xe2x80x9d, a supporting plate and xe2x80x9c16xe2x80x9d, a connecting part of an apparatus. As to the apparatus shown in FIG. 8, refer to microfilmed Japanese Utility Model Registration Application No. 61-135016 (1986) (Utility Model Kokai Publication JP-U-A-63-43427 (1988)), particularly its conventional art (FIG. 2).
At the outset, a resist is coated on a wafer and then exposed with an exposing apparatus. The resultant wafer 11 is held on a wafer chuck 12 and then rotated at a most appropriate number of rotation for equalizing the dimension of a pattern developed on the surface of the wafer without causing defects upon developing, and a developer is dropped by applying a spraying method or the like. After dropping, a paddle state of the developer cast up on the wafer to have a liquid thickness of about 2 mm is formed in order to progress developing without fault by maintaining the developer cast up on the wafer for a predetermined time, e.g., for about 60 seconds. Subsequently, the developer is splashed away from the wafer by high speed rotation followed by washing away with pure water and then the wafer is subjected to be dried while rotating.
Alternative to the rotary chuck with a stationary, straight axis of rotation, JP-U-A-63-43427, proposed a method wherein the chuck is rotated at a low speed while tiltedly swinging its rotational axis for distributing the developer and proceeding the developing.
In proportion to minimizing a pattern or enlarging the size of a wafer, the process margin for preparing a semiconductor has become narrower and narrowe. The above developing process without exception includes the following problems.
That is, it is desirable to make the width of a resist pattern formed after developing uniformly over the entire surface of the wafer, however, it is difficult to meet the requirement of enlarging the size of the wafer or minimizing the pattern simply by applying conventional means or equipments.
For this reason, the optimum combination including the dropping condition of the developer and the number of rotation (rotation speed) has been assessed through varying various parameters by trial and error, whereby an enormous time has been required for establishing new satisfactory conditions.
Similarly to the developing process, it can be concluded that next step of dry-etching process involves a problem that a vast developing time has been required for pattern-etching uniformly over the entire surface of the wafer.
In order to solve the above problem, if the uniformity of the on-surface pattern of the wafer can be changed partially simply by apparatus adjustment, it will be possible to grade up the on-surface uniformity of the resist in terms of its dimension, and in addition to shorten a time for evaluation and development.
The present invention has been achieved based on recognizing the above problems and findings thereafter. It is an object of the present invention to provide a resist developing process which can make the central pattern width narrower selectively (i.e., prevent widening) simply by apparatus adjustment (mechanical adjustment), in case where, otherwise under certain conditions, the pattern width of a wafer""s central portion becomes wider, thereby making it possible to grade up the on-surface uniformity and improving the performance.
It is another object of the present invention to provide a resist developing process which can serve as shortening a time for evaluation and development and grading up the productivity.
Other objects of the present invention will become apparent in the entire disclosure.
In order to attain the above objects, there is provided a novel resist developing process for forming a resist pattern on a wafer for semiconductor according to the present invention. The process comprises steps of puddling (casting up) a developer on the surface of a wafer, holding the wafer inclined at a predetermined angle while the developer is being puddled and repeating stoppage and slow rotation alternately plural times.
The pattern width at the central portion of the wafer can be made narrower as compared with the case where no such process is applied. Namely, otherwise the pattern width of the central portion of the wafer becomes wider than that of the peripheral portion of the wafer. Thus an increased pattern uniformity in the width over the entire wafer surface can be achieved.
The tilt angle is set at an angle which does not allow the developer to spill over the wafer. The slow rotation is carried out at a speed which allows the developer to be retained puddled on the wafer.
The stoppage of rotation is performed during a period of time which is sufficient to allow the developer to flow toward and puddle at the lowest end portion of the inclined wafer to provide a thinner thickness of the developer at the other end portion thereof.
The alternate stoppage and slow rotation are repeated until a uniform pattern width over the entire wafer is achieved.
Alternatively, the alternate stoppage and slow rotation are repeated sufficient times to give an increased developing rate at the control portion of the wafer as compared with the peripheral portion thereof.